[4.2.y-ckt stable] Patch "PKCS#7: pkcs7_validate_trust(): initialize the _trusted output argument" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    PKCS#7: pkcs7_validate_trust(): initialize the _trusted output argument

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 5e2d8c748035068f6c43135ea779af7b0faadf10 Mon Sep 17 00:00:00 2001
From: Nicolai Stange <nicstange at gmail.com>
Date: Sun, 20 Mar 2016 23:23:46 +0100
Subject: PKCS#7: pkcs7_validate_trust(): initialize the _trusted output
 argument

commit e54358915d0a00399c11c2c23ae1be674cba188a upstream.

Despite what the DocBook comment to pkcs7_validate_trust() says, the
*_trusted argument is never set to false.

pkcs7_validate_trust() only positively sets *_trusted upon encountering
a trusted PKCS#7 SignedInfo block.

This is quite unfortunate since its callers, system_verify_data() for
example, depend on pkcs7_validate_trust() clearing *_trusted on non-trust.

Indeed, UBSAN splats when attempting to load the uninitialized local
variable 'trusted' from system_verify_data() in pkcs7_validate_trust():

  UBSAN: Undefined behaviour in crypto/asymmetric_keys/pkcs7_trust.c:194:14
  load of value 82 is not a valid value for type '_Bool'
  [...]
  Call Trace:
    [<ffffffff818c4d35>] dump_stack+0xbc/0x117
    [<ffffffff818c4c79>] ? _atomic_dec_and_lock+0x169/0x169
    [<ffffffff8194113b>] ubsan_epilogue+0xd/0x4e
    [<ffffffff819419fa>] __ubsan_handle_load_invalid_value+0x111/0x158
    [<ffffffff819418e9>] ? val_to_string.constprop.12+0xcf/0xcf
    [<ffffffff818334a4>] ? x509_request_asymmetric_key+0x114/0x370
    [<ffffffff814b83f0>] ? kfree+0x220/0x370
    [<ffffffff818312c2>] ? public_key_verify_signature_2+0x32/0x50
    [<ffffffff81835e04>] pkcs7_validate_trust+0x524/0x5f0
    [<ffffffff813c391a>] system_verify_data+0xca/0x170
    [<ffffffff813c3850>] ? top_trace_array+0x9b/0x9b
    [<ffffffff81510b29>] ? __vfs_read+0x279/0x3d0
    [<ffffffff8129372f>] mod_verify_sig+0x1ff/0x290
    [...]

The implication is that pkcs7_validate_trust() effectively grants trust
when it really shouldn't have.

Fix this by explicitly setting *_trusted to false at the very beginning
of pkcs7_validate_trust().

Signed-off-by: Nicolai Stange <nicstange at gmail.com>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 crypto/asymmetric_keys/pkcs7_trust.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
index 1d29376..841a04c 100644
--- a/crypto/asymmetric_keys/pkcs7_trust.c
+++ b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -174,6 +174,8 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 	int cached_ret = -ENOKEY;
 	int ret;

+	*_trusted = false;
+
 	for (p = pkcs7->certs; p; p = p->next)
 		p->seen = false;

--
2.7.4